This invention generally relates to permanent wave rods which are used by hairdressers and the like during the application of a permanent solution to a person's hair. More particularly, this invention relates to the problem of hair slippage from around a permanent wave rod as a person giving a permanent to another attempts to roll the hair around the rod.
A conventional-type permanent wave rod is generally made of a rigid, non-porous and non-wettable cylindrically shaped plastic member (conventionally polyethylene) which is designed to be re-used from permanent to permanent. Also, such a conventional-type permanent wave rod generally has an axial bore therethrough and radially extending perforations through its outer circumferential surface which communicate with the bore therethrough.
The theory behind such a construction is that the hairdresser is supposed to inject a permanent wave solution into the central axial bore of the permanent wave rod which will then dispense through the perforations in the same and flow into the hair wrapped therearound. However, for all practical purposes, most hairdressers do not apply the permanent wave solution in such a manner as it is costly and time consuming. Rather, the hairdresser will simply apply the permanent wave solution to the hair directly from the outside of the permanent wave rod.
A large difficulty involved in giving a permanent is the actual rolling of the hair around the permanent wave rod itself. In order to facilitate winding the ends of the hair around the permanent wave rod, a special type of paper known as end paper is wrapped around the ends of the hair to hold them flatly together. This end paper has the characteristic of having a high tensile strength even when wetted so that tearing of the same will not occur as the hair and end paper are wrapped around the permanent wave rod. However, slippage between the end paper and the permanent wave rod often occurs making it very difficult and time consuming for the hairdresser since numerous wrappings around such wave rods are normally needed as a direct result of such slippage. I have found that one of the major causes of such slippage is due to the fact that conventional permanent wave rods have generally been made of a non-wettable material or have a water-resistant outer coating. Consequently, the end result is that the hairdresser may have to re-roll the entire permanent or portions thereof because the hair and end paper around a particular wave rod slipped and loosened, thereby causing an inconsistency in the tightness of the curls created.
Wettability is generally defined as the degree of which a solid may be wetted. In other words, wettability generally describes the degree to which a solid attracts or repels a liquid. The criterion generally employed to determine the wettability of a substance is to look at the contact angle between the solid and liquid (measured through the liquid) at a point where the outer surface of the liquid and the solid meet. If this angle is greater than 90.degree., the solid is considered relatively non-wettable, and the liquid will tend to ball up and roll off the solid surface. On the other hand, when the contact angle is less than 90.degree. the solid is considered wettable, and the liquid will tend to spread out over the solid. In sum, there is a greater attraction between wettable solids and liquids.
Generally, many factors are present which determine whether a particular material is wettable. However, even the experts in the field of Materials Engineering apparently disagree as to which factors are the most important ones to consider. One factor usually considered is the relative surface tension of a material, but this factor is not the exclusive factor to be considered. For example, polyethylene and polystyrene have nearly equal surface tensions, 31 vs. 33 dynes/em. Nevertheless, I have discovered that polystyrene is readily wettable, whereas polyethylene repels water and does not wet well at all. Thus, in this case, it appears that the critical surface tension of the materials is not the primary factor of importance.
It has been speculated that, due to the marked differences between the respective surfaces of polyethylene and polystyrene, and the fact that water acts somewhat as an adhesive, that these factors may be more significant in determining the reason for wettability in this case. As water displaces air between the interface of two materials, such as end paper and expanded polystyrene, the water acts as an adhesive. However, if the surface repels water, as polyethylene does, then I believe that there is less displacement of air by water, and consequently less adhesive effect by the water at the interface of the two materials.
In any event, and for whatever reason, I have discovered that the use of expanded polystyrene in the manufacture of permanent wave rods provides for greater adherence between the end paper and the permanent wave rods. I believe that the concept of wettability may be why conventional permanent wave rods have difficulty with slippage problems, since most conventional permanent wave rods are made of a material which is relatively non-wettable, such as polypropylene or polyethylene.
Various solutions to the problem have been implemented in the past in an attempt to prevent the slippage of the end paper from around the wave rod, the most common approach being to form such conventional-type wave rods with a multitude of tiny nodules protruding radially outwards from the surface of the rods so as to provide a better grip on the end paper. Nevertheless, this means of preventing slippage has not been successful in that slippage continues to occur, thereby causing increased time involved with giving a permanent to another person, as well as the higher cost involved because of the increased time spent for redoing those portions of the permanent which did not result in as tight of a curl as desired.
Another problem with the conventional-type permanent wave rod stems from the fact that it must be reused from person to person, and from permanent to permanent, in order to be cost effective. Because the conventional-type permanent wave rods are reused, they must be cleaned and disinfected between each permanent given so as to facilitate a sanitary working area. In fact, beauty salons and the like are commonly subjected to periodic inspections by government health officials for cleanliness of their tools which are used in hairdressing. Re-use of the conventional-type permanent wave rods also means that such permanent wave rods have to be stored between uses in a sanitary place.
Because of the problems inherent with the conventional-type permanent wave rods, there has been a long felt need for a permanent wave rod which can be inexpensively made and disposable after each permanent, thereby eliminating the necessary sanitization which is required with the conventional-type permanent wave rods. Also, a substantial need has been felt by the industry for a permanent wave rod that will prevent slippage of the end paper, and consequently the hair wrapped therein, from around the wave rod's circumferential surface.
I have found that the present invention solves both of these problems related to the use of conventional-type permanent wave rods, and offers other marked advantages as well, which are clear improvements over the prior art.